4842 - Automotive engines

Jake Stewart

Boyle’s law describes the relationship between the pressure and volume of gas in an enclosed space.

The law states "the pressure exerted by a gas held at a constant temperature varies inversely with the volume of the gas"

This is due to gas being made up of loosely space moluces which are free to move at random. When this gas is compressed in a small area these molecules are pressed together so the gas takes up less volume. Since the molecules have less space to move, the rapidly hit the walls of the enclosed area more frequently and this increases pressure.

This means the volume is doubled, the pressure is halved

And if the volume is halved, the pressure is doubled.

The mathematical equation for Boyle's law is:

Pressure = Constant/Volume
or
Volume = Constant/Pressure
or
Pressure x Volume = Constant

PV = P₁V₁

p denotes the pressure of the system.

V denotes the volume of the gas.

Boyle’s law relates to automotive engines particularly in the combustion chamber. According to this law a smaller area of combustion is better in terms of performance as high compression ratios will be achieved.

Charles law deals with the effect of heat on the expansion of gases.

Charles’s law states that if a given quantity of gas is held at a constant pressure, its volume is directly proportional to the absolute temperature.

This means that as the temperature of a gas increases in an enclosed area, the gas molecules will start to move around very quickly and hit the walls of the enclosed area with more force so the volume will increase.

The volume and temperature is very related, if the temperature was not sufficient the molecules would have trouble overcoming the forces of attraction among them and would not be able to fill the container.

If the temperature increases, the gas takes up more space. If the temperature decreases, the gas takes up less space.

Charles law equation can be written out as:

Temperature = Constant x Volume
or
Volume = Constant x Temperature
or
Volume/Temperature = Constant

V1/T1=V2/T2

An example of how Charles law equation:

Find the final volume of gas at 100 K, if the volume of gas is 5 L at 120 K.

V_i = 5 L, T_i = 120 K, T_f = 100 K

Substitute the values in the below volume equation:

Final Volume(V_f) = V_iT_f / T_i

= (5 x 100) / 120

= 500 / 120

Final Volume(V_f) = 4.167 L